warning: if statement has empty body

Clang Frontend
1

Clang is giving bogus warning for the following case. Taken from opencflite.

CFBag.c:946:92: warning: if statement has empty body
    if (CFDictionary || CFSet) CF_OBJC_FUNCDISPATCH0(__kCFHashTypeID, CFIndex, hc, "count");
                                                                                           ^
CFBag.c:958:91: warning: if statement has empty body
    if (CFSet) CF_OBJC_FUNCDISPATCH1(__kCFHashTypeID, CFIndex, hc, "countForObject:", key);
                                                                                          ^
CFBag.c:1024:116: warning: if statement has empty body
    if (CFDictionary) CF_OBJC_FUNCDISPATCH2(__kCFHashTypeID, Boolean, hc, "_getValue:forKey:", (any_t *)value, key);
                                                                                                                   ^

2

Why do you believe this is bogus? What does CF_OBJC_FUNCDISPATCH0 expand to, if anything? What is the preprocessed output (if you're using ccc, add -save-temps and look at CFBag.i)

Shantonu

3

never mind then.
  code expands to
  if (0) ;
So what is the purpose of this kind of coding.

4

For two reasons, first, there is a space following the closing ) on the condition, and second, because there is a word after the condition, before the ;.

5

It's just bad, CF_OBJC_FUNCDISPATCH? should expand to (void)0 or
`do { } while (0)` or anything similar that the compiler will optimize
out and is a valid expression, when it's meant to do nothing.

Defining it to expand to nothing is just bad. For example, had you
written something like:

`if (CF_OBJC_FUNCDISPATCH(...), 10)` it would result in a compilation
failure instead of just a warning. Arguably this kind of coding style is
even worse, but ...

6

Apparently, it looks like all this is last minute
hack because only part of the code was open sourced by Apple.

#define CFDictionary 0
#define CFSet 0
#define CFBag 0
#undef CFBag
#define CFBag 1

So things like the above violate all kind of coding style for Cocoa framework.
Why it was code this way in the first place is beyond my comprehension.

CF_OBJC_FUNCDISPATCH expands to (void(0)), if it is __WIN32__.

CoreFoundation in principle could be great standard library that goes with the C compiler (Clang).
but l am sure Apple wouldn't want that and license would preclude it too.
After seeing this kind of kludge, I am reluctant to advocate it.